U.S. patent number 11,358,092 [Application Number 17/014,796] was granted by the patent office on 2022-06-14 for acidic gas absorbent, acidic gas removal method and acidic gas removal apparatus.
This patent grant is currently assigned to KABUSHIKI KAISHA TOSHIBA, TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION. The grantee listed for this patent is KABUSHIKI KAISHA TOSHIBA, TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION. Invention is credited to Toshihiro Imada, Takashi Kuboki, Yoshihiko Nakano, Kenji Sano, Akiko Suzuki, Mitsuru Udatsu, Reiko Yoshimura.
United States Patent |
11,358,092 |
Suzuki , et al. |
June 14, 2022 |
Acidic gas absorbent, acidic gas removal method and acidic gas
removal apparatus
Abstract
The embodiments provide an acidic gas absorbent kept from
deterioration, an acidic gas removal method using the absorbent,
and an acidic gas removal apparatus using the same. The acidic gas
absorbent contains an amine compound and water, and further
contains superfine bubble containing inert gas wherein an average
diameter of said superfine bubble is 150 nm or less. The acidic gas
removal method provided here employs that absorbent. The acidic gas
removal apparatus is equipped with a unit for introducing the
superfine bubbles into the absorbent.
Inventors: |
Suzuki; Akiko (Ota,
JP), Nakano; Yoshihiko (Yokohama, JP),
Yoshimura; Reiko (Kawasaki, JP), Imada; Toshihiro
(Kawasaki, JP), Kuboki; Takashi (Ota, JP),
Sano; Kenji (Inagi, JP), Udatsu; Mitsuru
(Kawasaki, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA
TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION |
Tokyo
Kawasaki |
N/A
N/A |
JP
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
(Tokyo, JP)
TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION
(Kawasaki, JP)
|
Family
ID: |
1000006368469 |
Appl.
No.: |
17/014,796 |
Filed: |
September 8, 2020 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20210291108 A1 |
Sep 23, 2021 |
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Foreign Application Priority Data
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Mar 18, 2020 [JP] |
|
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JP2020-048107 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D
53/1475 (20130101); B01D 53/1493 (20130101); B01D
53/18 (20130101); B01D 53/1425 (20130101); B01D
2252/20447 (20130101); B01D 2252/20431 (20130101); B01D
2252/606 (20130101); B01D 2252/20489 (20130101); B01D
2252/608 (20130101); B01D 2252/504 (20130101) |
Current International
Class: |
B01D
53/14 (20060101); B01D 53/18 (20060101) |
References Cited
[Referenced By]
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2020-44492 |
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Mar 2020 |
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JP |
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Primary Examiner: Michener; Jennifer K
Assistant Examiner: Holecek; Cabrena
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. An acidic gas absorbent containing an amine compound, water and
superfine bubble containing inert gas wherein an average diameter
of said superfine bubble is 150 nm or less.
2. The acidic gas absorbent according to claim 1, wherein said
inert gas is selected from the group consisting of nitrogen,
helium, neon and argon.
3. The acidic gas absorbent according to claim 1, wherein said
superfine bubbles are contained in an amount of 1.times.10.sup.7 to
1.times.10.sup.12 bubbles per 1 mL.
4. The acidic gas absorbent according to claim 1, wherein said
amine compound is selected from the group consisting of primary
amines, secondary amines, tertiary amines and quaternary
ammoniums.
5. The acidic gas absorbent according to claim 1, wherein said
amine compound is contained in an amount of 3 to 80 mass % based on
the total mass of the acidic gas absorbent.
6. The acidic gas absorbent according to claim 1, which further
contains at least one additive agent selected from the group
consisting of oxidation inhibitors, pH adjusters, defoaming agents,
and anticorrosive agents.
7. An acidic gas removal method in which a gas containing an acidic
gas is brought into contact with the acidic gas absorbent according
to claim 1 so as to remove the acidic gas from the acidic
gas-containing gas.
8. An acidic gas removal apparatus comprising: an absorption unit
in which a gas containing an acidic gas is brought into contact
with an acidic gas absorbent containing an amine compound and
water, so that the absorbent absorbs the acidic gas to remove it
from the acidic gas-containing gas; a superfine bubble-introducing
unit in which superfine bubble containing inert gas wherein an
average diameter of said superfine bubble is 150 nm or less are
introduced into said acidic gas absorbent; and a regeneration unit
in which the absorbent holding the acidic gas is made to release
the acidic gas so as to be regenerated; so that the absorbent
regenerated in the regeneration unit is reused in the absorption
unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2020-048107, filed
on Mar. 18, 2020, the entire contents of which are incorporated
herein by reference.
FIELD
Embodiments of the present disclosure relate to an acidic gas
absorbent, an acidic gas removal method and an acidic gas removal
apparatus.
BACKGROUND
It has been recently pointed out that global warming is partly
attributed to greenhouse effect caused by increase of carbon
dioxide (CO.sub.2) concentration, and it is urgent to take
international measures to protect global environment. Carbon
dioxide (CO.sub.2) is largely generated by industrial activities,
and there is an increasing momentum toward reduction of CO.sub.2
emitted into the atmosphere. In particular, it is urgently
necessary to reduce CO.sub.2 emission from coal-fired power plants
and factories. Further, it is also desired to reduce emission of
acidic gases other than CO.sub.2, such as hydrogen sulfide
(H.sub.2S).
In view of that, as means for reducing emission of acidic gases
such as CO.sub.2, much attention is paid to not only streamlining
of thermal power plants or the like for emission reduction but also
CO.sub.2 recovery by use of chemical absorbents. As practical
chemical absorbents, amine compounds have been studied for a long
time. In carbon dioxide recovery systems, acidic gas absorbents
containing the amine compounds are generally regenerated and
cyclically used. In those cyclic uses, when absorbing or releasing
CO.sub.2, the acidic gas absorbents are often heated for
regeneration. However, in this procedure, the amine compounds tend
to be so denatured as to deteriorate the acidic gas absorbents by
the action of oxygen or the like contained in the acidic gas.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically shows an acidic gas removal apparatus
according to the embodiment.
DETAILED DESCRIPTION
The acidic gas absorbent according to an embodiment of the present
disclosure contains an amine compound and water, and further
contains superfine bubble containing inert gas wherein an average
diameter of said superfine bubble is 150 nm or less.
Further, in the acidic gas removal method according to another
embodiment of the disclosure, a gas containing an acidic gas is
brought into contact with the above acidic gas absorbent so as to
remove the acidic gas from the acidic gas-containing gas.
Furthermore, the acidic gas removal apparatus according to still
another embodiment of the disclosure comprises:
an absorption unit in which a gas containing an acidic gas is
brought into contact with an acidic gas absorbent containing an
amine compound and water, so that the absorbent absorbs the acidic
gas to remove it from the acidic gas-containing gas;
a superfine bubble-introducing unit in which superfine bubble
containing inert gas wherein an average diameter of said superfine
bubble is 150 nm or less are introduced into the above acidic gas
absorbent; and
a regeneration unit in which the absorbent holding the acidic gas
is made to release the acidic gas so as to be regenerated;
so that the absorbent regenerated in the regeneration unit is
reused in the absorption unit.
Embodiments will now be explained with reference to the
accompanying drawings.
<Acidic Gas Absorbent>
In the following description, the embodiments will be explained
mainly in case examples where the acidic gas is carbon dioxide
(CO.sub.2). However, the acidic gas absorbent according to the
embodiment can give the same effect on other acidic gases such as
hydrogen sulfide. Specifically, the absorbent of the embodiment is
suitable to absorb oxidizing gases such as carbon dioxide and
hydrogen sulfide. More specifically, the absorbent is particularly
suitable for absorbing carbon dioxide and is advantageously
employed in a system for recovering carbon dioxide from industrial
exhaust fumes.
The acidic gas absorbent according to the embodiment contains an
amine compound as a main agent for absorbing acidic gases. The
amine compound can be selected from known ones generally adopted as
acidic gas absorbents in consideration of the proper vapor
pressure.
Examples of the usable amine compounds include primary amines,
secondary amines, tertiary amines and quaternary ammoniums. In
addition, polyamine compounds such as diamines and triamines are
also employable. Further, it is still also possible to adopt
derivatives in which hydrogens in the above amine compounds are
replaced with substituents such as hydroxy or in which methylene
groups in the amine compounds are replaced with oxy, carbonyl,
sulfonyl or the like. Although amine compounds are water-soluble in
general, it is preferred to use amines having high
water-solubility.
Specifically, usable amine compounds are as follows:
(i) aminoalcohols,
(ii) cyclic amines,
(iii) primary amines,
(iv) secondary amines,
(v) tertiary amines,
(vi) polyamines,
(vii) polyalkylenepolyamines, and
(viii) amino acids.
Here, it should be noted that the above categories are only for the
sake of convenience, and there are some amine compounds included in
two or more of the above categories. For example,
methyldiethanolamine is a kind of aminoalcohol and is also a kind
of tertiary amine.
Among the above, it is preferred to adopt (i) aminoalcohols, (v)
tertiary amines, (vii) polyalkylenepolyamines or (viii) amino acids
because the diffusibility can be kept at a low level.
In the embodiment, it is preferred to adopt an amine compound
having a low vapor pressure. If the amine compound has a low vapor
pressure, it can be realized to keep the diffusibility thereof at a
low level. Specifically, the amine compound has a vapor pressure of
0.001 to 10 Pa, preferably 0.005 to 5 Pa, more preferably 0.01 to 1
Pa at 20.degree. C.
Preferred examples of the amine compound satisfying the above vapor
pressure condition include: methyldiethanolamine (vapor pressure at
20.degree. C.: 0.03 Pa), diethanolamine (vapor pressure at
20.degree. C.: 0.04 Pa), and ethyldiethanolamine (vapor pressure at
20.degree. C.: 0.3 Pa).
The acidic gas absorbent is repeatedly used, and hence the compound
preferably has high stability. In view of that, it is preferred not
to adopt ammonia or methylamine.
The acidic gas absorbent according to the embodiment also contains
water as a solvent, and hence is an aqueous solution in which the
above amine compound is dissolved or dispersed.
The acidic gas absorbent contains the amine compound in an amount
of preferably 3 to 80 mass %, more preferably 10 to 75 mass %,
further preferably 20 to 70 mass % based on the total mass of the
absorbent.
It is generally preferred for the amine concentration to be high in
view of energy consumption, plant scale and processing efficiency.
That is because carbon dioxide is absorbed and released in large
amounts per unit volume and further the rates thereof are high when
the amine compound is contained in a high concentration.
However, if the amine concentration is too high, the absorbent may
have increased viscosity and hence it is necessary to pay attention
to that. Nevertheless, if the content of the amine compound is
increased, it becomes possible for the absorbent to absorb carbon
dioxide in a sufficient amount at a satisfying rate and accordingly
to obtain excellent processing efficiency.
When adopted for recovering CO.sub.2, the acidic gas absorbent
containing the amine compound in an amount within the above range
is not only capable of absorbing CO.sub.2 in a large amount at a
high rate but also capable of releasing CO.sub.2 in a large amount
at a high rate. Accordingly, the absorbent has the advantage of
efficiently recovering carbon dioxide.
The acidic gas absorbent of the embodiment further contains
superfine bubbles. The term "superfine bubbles (e.g., ultrafine
bubbles)" in the embodiment means such minute bubbles having an
average diameter of 150 nm or less as to be invisible with the
eyes. Superfine bubbles have been under research and it is already
known that solutions containing superfine bubbles are useful as
detergents. Further, the present applicant has researched and found
that superfine bubbles in combination with the acidic gas absorbent
can prevent the amine compound from deterioration. In order to
obtain that effect efficiently, inert gas is adopted for forming
the superfine bubbles in the embodiment. The inert gas is
preferably nitrogen, helium, neon or argon, more preferably
nitrogen or argon. Among them, nitrogen is particularly preferred
because having the advantage of cost.
In the embodiment, the superfine bubbles have an average diameter
of 50 to 400 nm, preferably 150 nm or less. As for the number of
the superfine bubbles, the acidic gas absorbent contains preferably
1.times.10.sup.7 to 1.times.10.sup.12 bubbles, more preferably
1.times.10.sup.9 to 1.times.10.sup.11 bubbles per 1 mL of the
absorbent.
The average diameter and content (number) of the superfine bubbles
can be measured by various methods, such as, particle trajectory
analysis method, laser diffraction scattering method, dynamic light
scattering method, resonance mass measurement method, or method of
liquid dispersion stability evaluation. Among them, it is preferred
to adopt the particle trajectory analysis method or the laser
diffraction scattering method.
It is not clear the reason why the acidic gas absorbent containing
the superfine bubbles tends not to deteriorate, but the reason is
thought to be as follows. In the presence of the superfine bubbles,
oxygen is kept from dissolving in the absorbent. Further, dissolved
oxygen is easily released out of the absorbent by the action of the
superfine bubbles. Consequently, the acidic gas absorbent contains
such a small amount of oxygen that the amine compound is hardly
denatured. The acidic gas absorbent is thus presumed to be kept
from deterioration. In addition, the superfine bubbles are so
stably present in the acidic gas absorbent that they are hardly
released out of the solution, and accordingly the effect thereof
characteristically continues for a long time.
In the embodiment, the superfine bubbles can be introduced into the
acidic gas absorbent by use of any system. Examples of the system
include ultrasonic system, swirl flow system, pressure dissolution
system, and micropore system.
The acidic gas absorbent according to the embodiment contains the
above amine compound, the above superfine bubbles and water, and
can further contain other optional ingredients according to
necessity.
Examples of the optional ingredients include: water-soluble polymer
compounds, oxidation inhibitors, pH adjusters, defoaming agents,
and anticorrosive agents.
The water-soluble polymer compounds have effects of properly
controlling viscosity of the acidic gas absorbent and of improving
diffusibility of the amine compound. The water-soluble polymer
compound is preferably a water-soluble vinyl polymer or a
water-soluble polysaccharide. Examples of the water-soluble vinyl
polymer include: carboxy vinyl polymer, alkali metal salts of
carboxy vinyl polymer, polyvinyl alcohol, polyvinylpyrrolidone,
polyethylene glycol, and polyacrylic acid. Here, the "carboxy vinyl
polymer" includes polyacrylic acid, polymethacrylic acid,
polyacrylamide and copolymers thereof. The water-soluble
polysaccharide may be a synthesized or natural substance and is
preferably at least one selected from the group consisting of
cellulose, carboxymethyl cellulose, methyl cellulose, pectin, gum
arabic, alginic acid, and xanthan gum. Among them, cellulose is
preferred because of easy availability. Cellulose may be in the
form of cellulose nanofibers. The water-soluble polymer compound
has a mass average molecular weight of 900 to 200000, preferably
1000 to 180000.
The acidic gas absorbent contains the water-soluble polymer
compound in an amount of preferably 0.001 to 1 mass % based on the
total mass of the absorbent. The more the absorbent contains the
polymer compound, the more the diffusibility is improved. However,
if the polymer compound is contained too much, the absorbent may
have such a high viscosity as to be difficult to handle.
Preferred examples of the oxidation inhibitors include:
dibutylhydroxytoluene (BHT), butylhydroxyanisole (BHA), sodium
erythorbate, sodium nitrite, sulfur dioxide, 2-mercapto-imidazole
and 2-mercaptobenzimidazole. When the oxidation inhibitor is
incorporated, the amount thereof is preferably 0.01 to 1 mass %,
more preferably 0.1 to 0.5 mass % (provided that the whole amount
of the absorbent is regarded as 100 mass %). The oxidation
inhibitor can inhibit deterioration of the absorbent to extend the
working lifetime thereof.
Preferred examples of the defoaming agents include: silicone
defoaming agents and organic defoaming agents. When the defoaming
agent is incorporated, the amount thereof is preferably 0.00001 to
0.001 mass %, more preferably 0.0005 to 0.001 mass % (provided that
the whole amount of the absorbent is regarded as 100 mass %). The
defoaming agent can inhibit foaming of the absorbent so as to
prevent decrease of absorption and release efficiencies and to keep
the absorbent from degradation in fluidity and in circulation
efficiency.
Preferred examples of the anticorrosive agents include: phosphate
esters, tolyltriazoles, and benzotriazoles. When the anticorrosive
agent is incorporated, the amount thereof is preferably 0.00003 to
0.0008 mass %, more preferably 0.00005 to 0.005 mass % (provided
that the whole amount of the absorbent is regarded as 100 mass %).
The anticorrosive agent prevents corrosion of the plant facilities
to extend the working lifetime thereof.
There are no particular restrictions on the viscosity of the acidic
gas absorbent, but it is preferably 0.1 to 200 mPas, more
preferably 1 to 100 mPas at 25.degree. C. The water-soluble polymer
is incorporated so that the absorbent can exhibit sufficient
performance, and hence the acidic gas absorbent has a high
viscosity in general. However, if the viscosity is too high, the
absorbent has poor handling properties.
The viscosity of the absorbent can be measured by means of
VISCOMETER DV-II+Pro ([trademark], manufactured by BROOKFIELD).
<Acidic Gas Removal Method>
In the acidic gas removal method according to the embodiment, a gas
containing an acidic gas is brought into contact with the acidic
gas absorbent so as to remove the acidic gas from the acidic
gas-containing gas.
The acidic gas removal method of the embodiment basically
comprises: a step (absorption step) in which the aforementioned
absorbent of the embodiment is made to absorb an acidic gas; and
another step in which the acidic gas-holding absorbent of the
embodiment is made to release the absorbed acidic gas.
Specifically, the acidic gas removal method according the
embodiment essentially comprises: a step (acidic gas absorption
step) in which an acidic gas-containing gas (e.g., exhaust gas or
the like) is brought into contact with the acidic gas absorbent so
that the acidic gas is absorbed in the absorbent; and another step
(acidic gas separation step) in which the acidic gas-holding
absorbent obtained in the above acidic gas absorption step is
heated to release and remove the acidic gas from the absorbent. In
addition, since the above-described acidic gas absorbent of the
embodiment contains superfine bubbles, the method can further
contain a step in which the superfine bubbles are introduced into
the absorbent.
There are no particular restrictions on how an acidic
gas-containing gas is brought into contact with an aqueous solution
containing the above acidic gas absorbent. For example, the acidic
gas-containing gas may be bubbled and thereby absorbed in the
absorbent; the absorbent may be sprayed in the form of mist into a
stream of the acidic gas-containing gas (spray method); or
otherwise the acidic gas-containing gas may be brought into
countercurrent contact with the absorbent in an absorption unit
filled with a ceramic or metal mesh filler.
When the aqueous absorbent solution is made to absorb the acidic
gas-containing gas, the temperature of the absorbent is preferably
room temperature to 60.degree. C. or less, more preferably
50.degree. C. or less, further preferably 20 to 45.degree. C. The
lower the treating temperature is, the more the acidic gas is
absorbed. However, the lower limit of the treating temperature can
be determined according to the gas temperature in the process and
also to the heat recovery target or the like. The pressure in the
step of absorbing the acidic gas is normally near atmospheric
pressure. Although the pressure can be increased to enhance the
absorption performance, the process is preferably carried out at
atmospheric pressure so as to save energy consumption used for
compression.
In order to separate the acidic gas from the acidic gas-holding
absorbent and to recover pure or highly concentrated carbon
dioxide, the absorbent may be heated while the liquid interface
thereof is spread in a plate column, in a spray tower or in a
regeneration tower filled with a ceramic or metal mesh filler.
When the acidic gas is released, the acidic gas absorbent is kept
at a temperature of normally 70.degree. C. or more, preferably
80.degree. C. or more, further preferably 90 to 120.degree. C. The
higher the temperature is, the more the acidic gas is released.
However, in order to raise the temperature, it is necessary to
increase energy for heating the absorbent. Accordingly, the
temperature can be determined according to the gas temperature in
the process and also to the heat recovery target or the like. The
pressure in the step of releasing the acidic gas can be normally
set at about 1 to 3 atm.
After the acidic gas is released, the acidic gas absorbent can be
recycled and reused in the acidic gas absorption step. In addition,
heat generated in the step of absorbing the acidic gas is generally
cooled in a heat exchanger and used for preheating the aqueous
solution supplied to the regeneration unit where the solution is
processed for recycling.
The thus recovered acidic gas normally has a purity as high as 95
to 99 vol %. This pure or highly concentrated acidic gas can be
utilized as a material for synthesizing chemicals and/or polymers
or as a coolant for food freezing. Further, the recovered gas also
can be subjected to segregated storage in the ground or the like by
use of technologies under development.
The acidic gas absorbent according to the embodiment contains
superfine bubbles. As described above, the superfine bubbles
characteristically tend not to be released out of the acidic gas
absorbent. Accordingly, if used from the beginning, the acidic gas
absorbent containing superfine bubbles makes it possible to absorb
and recover the acidic gas for a long time. However, in the
long-term cyclic use, the superfine bubbles may decrease in the
acidic gas absorbent. In view of that, the method preferably
contains a step in which the superfine bubbles are introduced into
the absorbent. This means that, if necessary, the superfine bubbles
are continuously or intermittently introduced into the absorbent,
so as to ensure highly-efficient and long-term absorption and
recovery of the acidic gas. In the method containing the above
step, the acidic gas absorbent without superfine bubbles can be
initially prepared provided that the superfine bubbles are
thereafter introduced therein before used for absorbing the acidic
gas.
In that case, since being capable of inhibiting oxidation and
thermal deterioration of the acidic gas absorbent, the superfine
bubbles are preferably introduced therein immediately before the
procedure in which the acidic gas absorbent is heated and thereby
liable to deteriorate. Specifically, they are preferably introduced
immediately before the absorbent absorbs the acidic gas in the
absorption step or immediately before the absorbent is heated for
regeneration.
<Acidic Gas Removal Apparatus>
The acidic gas removal apparatus according to the embodiment
comprises:
an absorption unit in which a gas containing an acidic gas is
brought into contact with the aforementioned acidic gas absorbent,
so that the absorbent absorbs the acidic gas to remove it from the
acidic gas-containing gas;
a superfine bubble-introducing unit in which superfine bubble
containing inert gas wherein an average diameter of said superfine
bubble is 150 nm or less are introduced into the above acidic gas
absorbent; and
a regeneration unit in which the absorbent holding the acidic gas
is made to release the acidic gas so as to be regenerated;
so that the absorbent regenerated in the regeneration unit is
reused in the absorption unit.
FIG. 1 schematically shows the acidic gas removal apparatus
according to the embodiment.
The acidic gas removal apparatus 1 comprises: an absorption unit 2
in which a gas containing an acidic gas (e.g., exhaust gas) is
brought into contact with the acidic gas absorbent, so that the
absorbent absorbs the acidic gas to remove it from the acidic
gas-containing gas; and a regeneration unit 3 in which the
absorbent holding the acidic gas is made to release the acidic gas
so as to be regenerated. In the following description, the
explanation is given in case examples where the acidic gas is
carbon dioxide.
As shown in FIG. 1, a discharge gas containing CO.sub.2, such as, a
combustion exhaust gas emitted from a thermal power plant or the
like, is introduced through a gas inlet 4 into the lower part of
the absorption unit 2. The discharge gas is confined in the
absorption unit 2 and brought into contact with an acidic gas
absorbent supplied from an absorbent inlet 5 provided on the upper
part of the unit. As the acidic gas absorbent, the aforementioned
absorbent of the embodiment is employed.
In the way described above, as the result of contact with the
acidic gas absorbent, carbon dioxide is absorbed in the absorbent
and thereby removed from the discharge gas. After treated to remove
carbon dioxide, the discharge gas is emitted through a gas outlet 6
from the absorption unit 2.
The CO.sub.2-holding absorbent is then sent by a rich liquid pump 8
to a heat exchanger 7 and then to the regeneration unit 3. In the
regeneration unit 3, while the absorbent is moved down from the
upper part to the lower part, the acidic gas is released from the
absorbent and thereby the absorbent is regenerated.
The absorbent regenerated in the regeneration unit 3 is sent by a
lean liquid pump 9 to the heat exchanger 7 and an absorbent cooler
10, and then returned into the absorption unit 2 through the
absorbent inlet 5.
On the other hand, at the upper part of the regeneration unit 3,
the acidic gas released from the absorbent is brought into contact
with reflux water supplied from a reflux drum 11. The water is then
transferred out of the regeneration unit 3.
The CO.sub.2-containing reflux water is cooled with a reflux
condenser 12, and thereafter separated in the reflux drum 11 into
water and a liquid component condensed from water vapor
accompanying CO.sub.2. The liquid component is sent through an
acidic gas recovering line 13 for the step of recovering the acidic
gas. Meanwhile, the reflux water separated from the acidic gas is
sent into the regeneration unit 3.
The acidic gas removal apparatus 1 further comprises a superfine
bubble-introducing unit in which superfine bubble containing inert
gas wherein an average diameter of said superfine bubble is 150 nm
or less are introduced. This unit is for the purpose of introducing
the superfine bubbles into the acidic gas absorbent. As an example,
in the unit, superfine bubbles are initially introduced into water
or the like and thereafter the obtained liquid is mixed with the
acidic gas absorbent. As another example, in the unit, a portion of
the circulating absorbent is taken out and superfine bubbles are
introduced therein, and then returned to the bulk of the acidic gas
absorbent. The superfine bubbles may be introduced at once,
intermittently or continuously. In FIG. 1, the superfine
bubble-introducing unit 14 is provided upstream of the absorption
unit 2. In the apparatus having that constitution, the absorption
unit is supplied with the acidic gas absorbent in which dissolved
oxygen is reduced and therefore it becomes possible to keep the
absorbent from thermal deterioration in the absorption unit.
However, the installation point of the introducing unit is not
limited to the above. For example, the introducing unit can be
installed at the position A in FIG. 1, that is, upstream of the
regeneration unit 3, so as to keep the absorbent from thermal
deterioration in the regeneration unit. Further, the apparatus may
comprise two or more superfine bubble-introducing units.
The acidic gas removal apparatus 1 thus employs the acidic gas
absorbent excellent in acidic gas absorption and release
performance, and thereby makes it possible to absorb and remove
acidic gases efficiently.
Comparative Example 1
Methyldiethanolamine was dissolved in water to prepare an absorbent
of Comparative example 1, which contained methyldiethanolamine in
an amount of 45 mass %. The absorbent was bubbled with nitrogen for
1 hour, and then stored under atmosphere for a week. Subsequently,
the absorbent was sealed in an autoclave under atmosphere, and then
heated at 120.degree. C. for 24 hours. Before and after the
heating, the amine concentration was measured by gas
chromatography-mass spectrometry (GC/MS) to calculate the rate of
amine loss by heating.
Example 1
While being cooled with ice, methyldiethanolamine was dissolved in
water containing 1.41.times.10.sup.10 superfine nitrogen bubbles
having an average diameter of 73.4 nm, to prepare an absorbent of
Example 1, which contained methyldiethanolamine in an amount of 45
mass %. After the absorbent was stored under atmosphere for a week,
the superfine bubbles in the absorbent were measured with a
nanoparticle size analyzer SALD-7500nano X10 ([trademark],
manufactured by Shimadzu Corporation). In the measurement,
diffracted/scattered light intensity was measured with respect to
each of the absorbent containing the superfine bubbles and a
solvent without them (blank), so as to estimate the average
diameter from the difference between the results. Specifically,
first the blank sample was set in a batch cell and measured.
Subsequently, after the blank sample was evacuated, the absorbent
was poured into the batch cell with careful attention to avoid
bubbling and then stirred a few times with a stir bar. After
ripples and shimmers were confirmed to subside, the absorbent was
measured. The measurement was carried out three times, and the
results were averaged to determine the measured value. As a result,
the average diameter of the superfine bubbles was found to be 107
nm, and the number of the superfine bubbles contained in 1 mL of
the absorbent was found to be 8.1.times.10.sup.8. Meanwhile, the
absorbent was sealed in an autoclave under atmosphere, and then
heated at 120.degree. C. for 24 hours. From the amine
concentrations before and after the heating, the rate of amine loss
was calculated and found to decrease by 50% of that in Comparison
example 1.
Comparative Example 2
Piperazine was dissolved in water to prepare an absorbent of
Comparative example 2, which contained piperazine in an amount of
10 mass %. The rate of amine loss was calculated in the same manner
as in Comparative example 1.
Example 2
Pipearzine was dissolved in water containing 1.41.times.10.sup.10
superfine nitrogen bubbles having an average diameter of 73.4 nm,
to prepare an absorbent of Example 2, which contained pipearzine in
an amount of 10 mass %. After the absorbent was stored under
atmosphere for a week, the superfine bubbles in the absorbent were
measured in the same manner as in Example 1. As a result, the
average diameter of the superfine bubbles was found to be 120 nm,
and the number thereof contained in 1 mL of the absorbent was found
to be 10.1.times.10.sup.8. Further, the rate of amine loss was
calculated in the same manner as in Example 1 and found to decrease
by 70% of that in Comparison example 2.
While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to
limit the scope of the inventions. Indeed, the novel methods and
systems described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the methods and systems described herein may be made
without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fail within the scope and
sprit of the invention.
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